Graphene, one of the widely studied two dimensional materials, comprises a single layer of carbon atoms in a honeycomb lattice. It has special electrical, optical, and mechanical properties due to its tunable band dispersion relation and atomic thickness. Because of its unique band structure, graphene possesses very high mobility and fast carrier relaxation time,1-5 making it an attractive candidate for ultrafast electronics and optoelectronic devices such as transistors,6 optical switches,7-9 mid-infrared (mid-IR) photodeteetors,10 photovoltaic devices,11 saturable absorbers and ultrafast lasers12 etc. However, low optical absorbance (<2.5%) in the visible to IR wavelength range makes graphene an inefficient optical material. With such a low absorption cross-section, these approaches are not suitable for many applications.